In general, most cargo ships in maritime transport, excluding ships that perform a return voyage so as to exchange similar goods, perform one-way operation.
During the return voyage after one-way operation with full load condition, ballast water should be introduced into a ship so as to implement a balance of the ship, a safety, and an improved ship maneuverability, so that it is possible to leave on a voyage in a ballast condition.
In this case, the ballast water is filled from a harbor and is transported to a new harbor of other place where the ballast water is discharged. Thus, the release of marine organism and pathogen contained in the ballast water carried from distant location may be dangerous to both people and animal in the new harbor as well as harmful to a new environment.
When non-natural marine life is introduced into a new ecosystem, it may cause a devastating effect to natural flora and fauna that may not have a natural defense system against new species. In addition, harmful bacterial pathogens, such as cholera, may exist in the original harbor. Such a pathogen may be proliferated in a ballast tank over time, so that disease may break out in an area where the pathogen is released.
A risk posed by such marine life and pathogens may be controlled by killing the above species existing in the ballast water.
An electrolytic method that treats ballast water by using sodium hypochlorite generated by electrolyzing sea water is widely used for the method for killing organisms.
However, because the treating of the ballast water by using the above mentioned electrolytic method should convert NaCl contained in seawater into NaClO, this treating of the ballast water is easy in a sea water area, but when a ship sails in a freshwater area such as river (in particular, in an area where salt concentration is 0.5 psu or less), it is impossible to use the electrolytic method.
Alternatively, in addition to the electrolytic method, in order to maintain the efficiency of the ballast water treatment in a freshwater area, there is a method of killing the ballast water through an injection of a chemical, such as a germicide.
Because NaDCC is cheap and has a strong sterilizing power among the germicides, it is widely used in a sterilization treatment.
However, NaDCC should be treated very carefully, as it causes a severe stimulus to the eyes, is toxic if breathed in, and is harmful if swallowed.
Also, because an aqueous solution type NaDCC has a large volume and is degraded according to temperature, a suitable place where it can be used is limited and it is hard to treat a large amount for proper storage.
Additionally, a granule type NaDCC has handling difficulty because it is easily scattered in the form of dust. Therefore, when supplementing the granule type NaDCC, an expert who is equipped with safety equipment should perform the operation, thus leading to longer operation times. Furthermore, because the NaDCC dust is liable to be scattered, a separate ventilator is needed such that the overall system becomes more complex and larger.